for my $d ( 30 .. 36 ) {
  my $this = $nil->text2digest( ( 'a' x $d ) . 'b' ) ;
  my $that = $nil->text2digest( ( 'a' x ( $d + 1 ) ) ) ;
  print nilcomp( $this , $that ) ;
  }

sub nilcomp {
  my $diff = 0 ;
  my $diff2 = 0 ;
  my @this = split /|/ , shift ;
  my @that = split /|/ , shift ;
  for my $a ( 0 .. scalar(@this)-1 ) {
    $diff++ if $this[$a] ne $that[$a] ;
    my $is = hex $this[$a] ;
    my $at = hex $that[$a] ;
    if ( $is != $at ) {
      $diff2 += abs $is - $at ;
      }
    }
  return ( join "" , @this) . qq(\n) .
         ( join "" , @that) . qq(\n) .
         $diff . qq( characters different\n) .
         ( abs $diff2 ) . qq( bits different\n\n);
  }